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Give three important minerals that rocks contain
i. Quartz which is sometimes called Silica. this is a compound of Silicon and
oxygen and is a very common mineral
ii. Felspars which are compounds of Potassium, sodium, calcium
iii. Micas which are compounds of Potassium, magnesium, silicon and
aluminum.
Explain how the following groups of rocks were formed, and for each group give at least
two examples (1996) (1986) (2001)
i. Sedimentary rocks
These are rocks which were formed through the collection of sediments.
They are formed through the collection of clastic sediments, non clastic
sediments and organic sediments when transported, deposited, compacted
and lithified. Examples of sedimentary rocks are conglomerate, Breccias,
sandstone, shale, Limestone
ii. Igneous rocks
These are rocks formed through the cooling and solidification of molten
material called magma. Those formed after magma solidifies and cools on
the earth’s surface are called volcanic or extrusive while those formed
within the earth’s crust are called intrusive.
Examples include granite, diorite, gabbro, basalt, andesine, peridotite,
punice and scoria.
iii. Metamorphic rocks
These are rocks which are originally igneous or sedimentary but have
changed into character and appearance due to application of intense heat,
pressure, water and air.
Examples include: slate, schist, phyllite, gneiss, quartzite and serpentine.
Mention three characteristics of each group of rocks motioned above
i. Characteristics of sedimentary rocks:
- They occur in layers, that is, they are stratified
- They contain fossils, that is , they are fossilized
- They are non-crystalline, that is, they do not contain crystals
- They are generally soft rocks.
ii. Characteristics of igneous rocks
- They are crystalline in nature, that is, they form crystals
- They are not stratified thus they do not occur in layers
- The rocks are non fossiferous, that is, they do not contain fossils
iii. Characteristics of metamorphic rocks